Characterization of a novel erythropoiesis-inhibiting human protein

Coexistent Polycythemia Vera and Chronic Lymphocytic Leukemia: Down-Regulation of Myeloid Clone by the Lymphoid Clone?

Coexistence of polycythemia vera (PV) and chronic lymphocytic leukemia (CLL) is a rare association. The clinical course in all cases has been remarkably mild, thus suggesting suppression and/or control of each disease by the other. We have studied a patient who exhibited a typical feature of PV for 6 years. After 3 years of remission, induced by (32)P, a mild form of PV reappeared in association with B-CLL. In order to investigate the possible influence of CLL to the mild expression of PV, we have performed several in vitro colony assays and the tumor necrosis factor (TNF) assay. Colony formation by patient's bone marrow hematopoietic progenitor cells showed "spontaneous" BFU-E and CFU-E. In addition, patient's plasma selectively inhibited growth of normal BFU-E and CFU-E colony formation. TNF bioactivity, analysed during the course of the disease, was reduced. These findings suggested the existence of an inhibitor of erythropoiesis that could be involved in a down regulation of the myeloid clone by the lymphoid clone in this patient.

The activation of inactive membrane-associated protein kinase C is associated with DMSO-induced erythroleukemia cell differentiation

The rapid redistribution of cytosolic protein kinase C (PKC) to membranes and its subsequent proteolytic activation to PKM have been implicated in the DMSO/HMBA-induced differentiation of murine erythroleukemia (MEL) cells. However, DMSO was found not to induce detectable changes in PKC distribution in a MEL cell subline (MEL1) which differentiated normally in response to the agent. Nevertheless, the differentiation of MEL1 cells appeared dependent on an early PKC-related event because hemoglobinization was partially blocked by the PKC inhibitor H-7 added to cells within the first 2 h after DMSO induction. Indeed, a rapid (15-60 min) increase in membrane PKC activity was detected in DMSO-treated MEL1 cells using a novel method which quantitates the amount of 'active' PKC in intact membranes. This transient PKC increase resulted from the activation of 'inactive' enzyme already associated with membranes, and not from the translocation of cytosolic PKC. Conventional PKC assays cannot distinguish between active and inactive membrane PKC pools. DMSO also activated inactive membrane PKC in HL-60 cells, but not in S49T-lymphoma and WEHI-231 B-lymphoma cells which do not differentiate in response to DMSO. The results suggest that a rapid and transient increase in membrane PKC activity may be an important early step in DMSO-induced differentiation of erythroleukemia cells.